a) Field of the Invention
The invention relates to a device for transporting and for handling microtiter plates, wherein by microtiter plates is meant standardized carriers for specimens to be examined and/or processed for development of pharmaceutic agents in medical diagnoses or the like.
b) Description of the Related Art
The prior art in this field is substantially set forth in the following publications:    1. “Accelerating Drug Discovery Process with Automation and Robotics in High Throughput Screening”, Ed.: John P. Delvin, 1997 Marcel Decker Inc., ISBN 0-8247-0067-8;    2. Examples in “Laboratory Automation News”, Ed.: Robin A. Felder, Health Sciences Center Charlottesville, Va. 22908;    3. “Microplate Standardization Report 3”, Journal of Biomolecular Screening, Vol. 1, No. 4, 1996;    4. “Spektrum der Wissenschaft Spezial Nr. 6”, Pharmaforschung 1997, Spektrum der Wissenschaft Verlagsgesellschaft mbH, Heidelberg, ISSN 0943-7096 . . . ;    5. “Industrieroboter [Industrial Robots]”, Kreuzer/Lugtenburg/MeiBner/Trukenbrodt 1994, Springer Verlag ISBN 3-540-54630-8.
The following abbreviations will be used hereinafter:                HTS high throughput screening        MTP microtiter plate        SPS stored program control.        
The analysis of a large number of specimens is a recurring task in the development of pharmaceutic substances as well as in medical diagnoses.
The development of a new pharmaceutic substance is a process extending over a number of years and incurring high costs. In this process, a suitable pharmacogenic substance is sought as target structure (target) (see prior art reference 4). By means of a suitable biochemical determining reaction (assay), reactions between targets and suitable bonding partners can be detected quantitatively.
There currently exist in the pharmaceutics industry libraries of active agents with from 300,000 to 1,000,000 different pure substances. With each new target, bonding partners or ligands must be identified from these substances with a suitable assay. This process is known as high throughput screening (HTS). A screening of this kind results in a small quantity of substances (typically 0.5% to 1% of the total number) showing a positive reaction in the assay. These cardinal structures represent the basis for the continued development of a medication.
In medical diagnoses, similar problems result when infections, diseases, genetic disposition and the like are to be determined through analysis of a number of individual specimens (in this case mostly blood specimens, urine specimens, and so on) based on standardized determining reactions. An example of this would be screening in blood banks of donor blood for infections and routine examinations in risk groups for infections or other symptoms of illness.
Another area of application in the field of biochemistry is combinatorial chemistry. In this case, several hundred different individual substances are generated simultaneously by parallel synthesis and must be processed and characterized subsequently by suitable techniques.
A specimen carrier standard has been developed for parallel processing of large quantities of specimens: microtiter plates (MTP) with standardized dimensions and 96-well, 384-well and 1536-well grids (see prior art reference 3). This arrangement enables parallel processing of many individual specimens. Analysis for such MTPs is carried out by automatic running of assay protocols. A protocol of this kind comprises a fixed quantity of processing steps, including, for example, dissolving and mixing of substances, incubating for a fixed period of time and determining measurement values by means of a suitable analyzing device. For this purpose, there are automated specimen processing devices (see prior art reference 2) for dissolving, pipetting, mixing, incubating, and measuring.
Typical HTS systems are laboratory devices which are linked together by a central handling system. Such a handling system essentially comprises a robot with grippers for MTP which transports the plates between individual stations either in a circular movement (revolving-sliding arm) or straight-line movement.
The running of individual work steps is regulated by software control (scheduler) which optimizes the flow of process steps with respect to any existing boundary conditions (e.g., plate may only be transferred to a free position; fixed time intervals must be maintained between successive process steps, etc.).
The performance or efficiency of such handling systems is limited because in most cases the robot arm is not located in the position in which the next operation is to be carried out. The time required for arriving at that position depends on the last operation carried out and is therefore not always the same.
A robot arm requires three movements to advance two plates by one position. The above-mentioned limitation must be taken into account by the software controlling the total system.
In order to link the process steps in a linear manner, it is necessary to adhere to the boundary condition of maintaining fixed time intervals between two processing steps for all operations.
In rotary cycles (revolving-sliding arm), the number and size of the components taking part in the process are limited, but paths are short. On the other hand, when moving on a straight line, the idle times in which the arm moves to the next position become increasingly longer as the length increases.
The control of a system of this kind is coordinated by the scheduler, that is, a program which calculates the flow of control commands with respect to time in such a way that every MTP undergoes the same treatment (process steps and process duration). There are two types of scheduler:
Static schedulers are those in which the flow of control commands with respect to time is calculated before the start of the process and is not updated.
Dynamic schedulers are those in which the flow of control commands with respect to time is calculated before the start of the process and continuously recalculated when there are deviations.
Dynamic schedulers can respond to changes resulting from slight disturbances or variations in the process, but at the cost of identical treatment of all plates. Both types of schedulers must carry out very complex optimizing resulting from the above-mentioned boundary conditions of the transport systems as currently used in HTS.